i made a schematic for an undocumented version of Gibson EH150

[The Amp Surgeon]

I created a schematic for an unchanged 1938 Gibson EH-150, never serviced, no orig parts changed, untouched innards that is different than the two versions I can find on-line. Where should I post? Sure could help someone trying to restore one like this that had been modified over the years. Attached. Feel free to share wherever. Thanks!

[Stevem]

Share this at Schematic heaven .
They will put it up there.

[sluckey]

V3 cannot operate properly without a ground reference for the grid.

[martin manning]

V3 should be connected like this...

[sluckey]

I think this is the original from the Gibson Amplifier Master Service Book...

[The Amp Surgeon]

V3 cannot operate properly without a ground reference for the grid.

Seemingly so, but yet, I checked, and checked thoroughly. Did you see my note about that on the schematic? I had checked for any voltage on the grid: there wass none. I had re-verified that there is no ground reference. Since no ground ref presents an extremely high Z node at grid of V3, I expected excess hum, but when I hung a 1M to ground on it, surprisingly there was not hum diff. I also grounded lug 1 of the pot, and that did not matter either. I have seen Gibson wire these and some BR series like that before, and grounding HAS made a diff. Why the volts at the grid don't run away on this mystifies me.

[The Amp Surgeon]

V3 should be connected like this...

Yes, well aware. See my note on the schematic? And i'll copy this from what I posted to another member: "Seemingly so, but yet, I checked, and checked thoroughly. Did you see my note about that on the schematic? I had checked for any voltage on the grid: there wass none. I had re-verified that there is no ground reference. Since no ground ref presents an extremely high Z node at grid of V3, I expected excess hum, but when I hung a 1M to ground on it, surprisingly there was not hum diff. I also grounded lug 1 of the pot, and that did not matter either. I have seen Gibson wire these and some BR series like that before, and grounding HAS made a diff. Why the volts at the grid don't run away on this mystifies me."

[The Amp Surgeon]

I think this is the original from the Gibson Amplifier Master Service Book...

Yes, I used part of that one which matched the unit in for service to create the correct schematic for the untouched unit I was drafting, since mine was so different.

[sluckey]

With both volume controls set max CCW, measure resistance from chassis to pin 4 and pin 5 of the 6N7. Connect the meter directly to the tube socket. What have you.

[The Amp Surgeon]

Share this at Schematic heaven .
They will put it up there.

I don't see how to submit items to Schematic Heaven. Can you help? Thanks.

[The Amp Surgeon]

With both volume controls set max CCW, measure resistance from chassis to pin 4 and pin 5 of the 6N7. Connect the meter directly to the tube socket. What have you.

Thanks; there is no 6N7 on the unit I am servicing. See my schematic. There is "infinite" resistance at the grid of V3 to ground, on mine.

[sluckey]

Thanks; there is no 6N7 on the unit I am servicing. See my schematic. There is "infinite" resistance at the grid of V3 to ground, on mine.

That's my mistake for looking at the wrong schematic while typing. Of course I meant your V3 grid that is floating. This is against everything I was taught about tube circuits in tech school back in '68. I'd love to see some hi-rez gut shot pics of that amp. I did a google search on the topic. Good to see that Google's AI believes the same theory that was taught back in the '60s.

[martin manning]

V3 should be connected like this...

...Why the volts at the grid don't run away on this mystifies me."

Did you happen to measure the idle current with and without the pot ground referenced? You could get that by measuring Vk. Trying to measure Vg will provide a ground reference and change the operating point. With the grid floating, the tube should become a diode with current limited by the plate and cathode resistors.